Main wing structure

ABSTRACT

A main wing structure comprises at least a leading edge structure and a wing central structure coupled to each other, and has a particular laminar-flow airfoil. The laminar-flow airfoil includes an upper wing surface, a lower wing surface, a leading edge and a trailing edge. The upper wing surface includes: a front profile portion which has a positive curvature radius, and which is provided to extend from the leading edge to a largest-thickness point located at 38% of a wing chord length; a central profile portion which has a positive curvature radius, and which is provided to extend from the largest-thickness point to the vicinity of a position corresponding to approximately 90% of the wing chord length at which a value obtained by dividing a thicknesswise difference between the position and the largest-thickness point by a distance in a direction of a wing chord from the largest-thickness point is equal to or smaller than 0.12; and a rear profile portion which has a negative curvature radius, and which is provided to extend from the vicinity of a position corresponding to approximately 95% of the wing chord length to the trailing edge. Coupled portions between the leading edge structure and the wing central structure are arranged at positions corresponding to approximately 20% of the wing chord length. Thus, it is possible to minimize an increase in drag due to a gap and a step between the coupled portions between the leading edge structure and the wing central structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present nonprovisional application claims priority under 35 USC 119to Japanese Patent Application No. 2002-0170787 filed on Jun. 12, 2002the entire contents thereof is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a main wing structure having aparticular laminar-flow airfoil and including at least a leading edgestructure and a wing central structure coupled to each other.

2. Description of the Related Art

A boundary layer on a surface of a main wing of an airplane is alaminar-flow boundary layer at a leading edge, but changes from thelaminar-flow boundary layer to a turbulent-flow boundary layer toward atrailing edge. A friction drag on the surface of the main wing issmaller at the laminar-flow boundary layer than at the turbulent-flowboundary layer. For this reason, in order to decrease the drag on themain wing, it is desirable that a transition point at which thelaminar-flow boundary layer changes to the turbulent-flow boundary flowis displaced toward the trailing edge, to thereby extend the region ofthe laminar-flow boundary layer as much as possible.

A laminar-flow airfoil of “6-series” developed by NACA in early 1940scan suppress the drag better than the conventional laminar-flow airfoil.However, when a portion of a wing surface in the vicinity of a leadingedge is rough, the largest lift disadvantageously tends to decreaselargely, leading to a great problem during takeoff or landing of theairplane.

Thereafter, NASA developed NLF(1)-0215F and NLF(1)-0414F in 1977 and1983, respectively. These laminar-flow airfoils enables a reduction inthe drag, but have a problem of causing a large head-lowering pitchingmoment. Moreover, because these laminar-flow airfoils are for use in alow-speed range, they have a problem of causing drag-divergencephenomenon at an early stage, of a subsonic speed range.

In HSNLF (1)-0213 developed by NASA in 1984 for use in a high subsonicspeed range, a drag-divergence phenomenon is difficult to generate, anda head-lowering pitching moment is small. However, the largest lift in alower Reynolds number range is small and the capacity of an inner-wingfuel tank is insufficient because the wing thickness is about 13% of awing chord length, leading to a difficulty in ensuring mileage.

A main wing structure of an airplane is constructed from at least aleading edge structure and a wing central structure coupled to eachother. Each structure is assembled separately in advance. It isconventionally unavoidable that a small gap and a small step generatedbetween the coupled portions cause an increase in drag. The laminar-flowairfoil is formed to provide a decrease in drag, which is one of itsmain objects, and hence it is desired that the increase in drag due tothe small gap and the small step generated between the coupled portionsis minimized.

SUMMARY AND OBJECTS OF THE INVENTION

Accordingly, it is an object of the present invention to minimize anincrease in drag due to a small gap and a small step generated betweencoupled portions between a leading edge structure and a wing centralstructure, in a main wing structure having a particular laminar-flowairfoil and including at least a leading edge structure and a wingcentral structure coupled to each other.

To achieve the above object, according to the present invention, thereis provided a main wing structure comprising at least a leading edgestructure and a wing central structure coupled to each other, whereinsaid main wing structure has a laminar-flow airfoil comprising an upperwing surface, a lower wing surface, a leading edge and a trailing edge,said upper wing surface including: a front profile portion which has apositive curvature radius, and which is provided to extend from theleading edge to a largest-thickness point located in a range of 30% to50% of a wing chord length; a central profile portion which has apositive curvature radius, and which is provided to extend from thelargest-thickness point to the vicinity of a position corresponding toapproximately 90% of the wing chord length at which a value obtained bydividing a thicknesswise difference between the position and thelargest-thickness point by a distance in a direction of a wing chordfrom the largest-thickness point is equal to or smaller than 0.12; and arear profile portion which has a negative curvature radius or isrectilinear, and which is provided to extend from the vicinity of aposition corresponding to approximately 95% of the wing chord length tothe trailing edge and wherein coupled portions between said leading edgestructure and said wing central structure are arranged at positionscorresponding to approximately 20% of the wing chord length.

With the above arrangement, the largest-thickness point at a rear end ofthe front profile portion on the upper wing surface of the laminar-flowairfoil of the main structure is established at a position whichcorresponds to a range of 30% to 50% of the wing chord length and whichis closer to the leading edge than in the conventional laminar-flowairfoil. Therefore, the pressure gradient in the central profile portionextending from the largest-thickness point toward the trailing edge isgentler than that in the conventional laminar-flow airfoil, therebystabilizing a turbulent-flow boundary layer and suppressing theoccurrence of the undesirable turbulent-flow boundary layer separationto achieve an increase in lift and a decrease in drag. In addition, therear profile portion which has the negative curvature radius (or whichis rectilinear) is provided to extend from the position corresponding to95% of the wing chord length on the upper wing surface to the trailingedge, thereby suddenly reducing the speed of air flow at the rearprofile portion, to positively promote the turbulent-flow boundary layerseparation. As a result, it is possible to decrease the lift in thevicinity of the trailing edge of the laminar-flow airfoil, to therebydecrease the head-lowering pitching moment.

In the main wing structure using the laminar-flow airfoil having theabove-described characteristic, the coupled portions between the leadingedge structure and the wing central structure are arranged at thepositions corresponding to approximately 20% of the wing chord length.Therefore, an increase in drag due to a gap and a step between thecoupled portions can be minimized, which can contribute to a reductionin fuel consumption.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 is a diagram showing a laminar-flow airfoil according to thepresent invention;

FIG. 2 is an enlarged diagram of a portion indicated by an arrow 2 inFIG. 1;

FIG. 3 is a diagram showing a theoretic design pressure profile in thelaminar-flow airfoil according to the present invention;

FIG. 4 is a graph showing experimental values and theoretic values for acharacteristic of the pitching moment coefficient Cm relative to a liftcoefficient Cl;

FIG. 5 is an exploded sectional view of coupled portions of a leadingedge structure and a wing central structure of a main wing;

FIG. 6 is an enlarged sectional view of the coupled portions of theleading edge structure and the wing central structure of the main wing;and

FIG. 7 is a graph showing the relationship between the sizes of steps onan upper wing surface and the amounts ΔCd of change in drag coefficientrelative to those in the positions of the steps.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described by way of a preferredembodiment with reference to the accompanying drawings.

Referring first to FIG. 1, the profile of a laminar-flow airfoilaccording to the present embodiment is comprised of an upper wingsurface Su, a lower wing surface S1, a leading edge E1 and a trailingedge Et. A largest-thickness position Tu on the upper wing surface SUmeasured from a cord line lies at a point corresponding to 38% of a wingchord length C in the present embodiment, to form a laminar-flowboundary layer region. A transition point TPu, at which the laminar-flowboundary layer region changes to a turbulent-flow boundary layer region,exists in the vicinity of the largest thickness position Tu. Thetransition point TPu lies near a position corresponding to 42% of thewing chord length C. A largest-thickness position T1 on the lower wingsurface S1 measured from the cord line lies at a point corresponding to49% of the wing chord length C in the present embodiment, to form alaminar-flow boundary layer region. A transition point TP1, at which thelaminar-flow boundary layer region changes to a turbulent-flow boundarylayer region, exists in the vicinity of the largest thickness positionT1. The transition point TP1 lies near a position corresponding to 63%of the wing chord length C.

The reason why the positions of the transition points TPu and TP1 aredetermined to be “near” the positions in the wing chord length C is thatthey change depending on flight conditions such as a Reynolds number, aMach number and a flight attitude.

In a conventional laminar-flow airfoil, e.g., a laminar-flow airfoil ofNACA “6-series,” the lengths of laminar-flow boundary layer regions onan upper wing surface Su and a lower wing surface S1 are generallydetermined to be the same, and a position of the transition point isdetermined to be a point corresponding to about 50% of a wing chordlength C. On the other hand, in the laminar-flow airfoil according tothe present embodiment, a stalling characteristic is improved byadvancing the largest-thickness position Tu on the upper wing surface Suto a position corresponding to 38% of the wing chord length C, i.e., byadvancing the position of the transition point TPu associated with thelargest-thickness position Tu to the vicinity of a positioncorresponding to 42% of the wing chord length C. Moreover, an increasein drag because of the advanced position of the transition point TPu onthe upper wing surface Su is compensated for by a decrease in dragprovided by retracting the largest-thickness position T1 on the lowerwing surface S1 to a position corresponding to 49% of the wing chordlength C, i.e., by retracting the position of the transition point TP1associated with the largest-thickness position T1 to the vicinity of aposition corresponding to 63% of the wing chord length C.

A region from the leading edge E1 to the largest-thickness position Tuon the upper wing surface Su forms a front profile portion Cf whichforms the laminar-flow boundary layer. The front profile portion Cf hasa positive curvature radius, and is curved convexly outwardly.

A region from the largest-thickness position Tu to the vicinity of apoint corresponding to 90% of the wing chord length C on the upper wingsurface Su forms a central profile portion Cc in the present invention.In the central profile portion Cc, the turbulent-flow boundary layerchanged from the laminar-flow boundary layer is developed. The centralprofile portion Cc has a positive curvature radius, and is curvedconvexly outwards. In the central profile portion Cc, however, a value(Δt/L) obtained by dividing a thicknesswise difference Δt between afront point in the central profile portion Cc (the point of 38%corresponding to the largest-thickness position Tu) and a rear point inthe central profile portion Cc (the point of 90%) by a distance L in adirection of a wing chord from the largest-thickness position Tu (theposition of 38% corresponding to the front point in the central profileportion Cc) to the rear point in the central profile portion Cc, is setto be equal to or smaller than 0.12. Namely, the central profile portionCc is inclined gently from the front point toward the rear point.

As a result, as can be seen from FIG. 3, the pressure gradient in thecentral profile portion Cc of the upper wing surface Su is recoveredgently from a negative pressure towards a positive pressure, so that theturbulent-flow boundary layer on such a portion can be stabilized andprevented from being separated, thereby preventing a reduction in liftand an increase in drag. If the largest-thickness position Tu ispositioned more to the rear than the above-described position in thelaminar-flow airfoil according to the present embodiment and as a resultthe pressure gradient in the central profile portion Cc becomes steep,the turbulent-flow boundary layer may be unstable and accidentallyseparated at any position in the central profile portion Cc, therebycausing a reduction in lift and an increase in drag. Specifically, thecloser the separation point becomes to the leading edge E1, moresignificant the reduction in lift and the increase in drag become.

As can be seen from FIG. 2 which is an enlarged diagram of a portion inthe vicinity of the trailing edge Et of the laminar-flow airfoilaccording to the present embodiment, a rear profile portion Cr providedin an area extending from the position corresponding to 90% of the wingchord length C to the trailing edge Et has a negative curvature radius,and is curved concavely outwards. As can be seen from FIG. 3, the speedof an air flow is reduced suddenly in the rear profile portion Cr havingthe negative curvature radius, whereby the pressure gradient in theportion Cr is steep to cause a sudden pressure recovery from thenegative pressure to the positive pressure. Thus, the separation of theturbulent-flow boundary layer is promoted in the vicinity of the rearprofile portion Cr, whereby the lift in the vicinity of the trailingedge Et is decreased, so that a head-lowing pitching moment about anaerodynamic center AC is decreased. A moment arm from the aerodynamiccenter AC existing at a position corresponding to 25% of the wing chordlength C to the trailing edge Et is longer, and hence even if the liftin the vicinity of the trailing edge Et is decreased slightly, thehead-lowing pitching moment is decreased remarkably.

When the head-lowing pitching moment is decreased in the above manner, anegative lift generated by a horizontal empennage for maintaining abalance around a pitching axis can be decreased. Thus, it is possible toprevent a decrease in the lift for the entire airplane due to thenegative lift generated by the horizontal empennage, and an increase inthe drag on the horizontal empennage which would otherwise increase thedrag on the entire airplane. Further, it is possible to eliminate theneed for increasing the moment arm from a gravity center position to thehorizontal empennage, thereby avoiding an increase in weight and anincrease in drag. Moreover, the separation occurring at the rear profileportion Cr is slight, so that a decrease in lift and an increase in dragdue to the separation do not matter.

FIG. 4 is a diagram for explaining an effect of decreasing thehead-lowering pitching moment. In FIG. 4, the circle indicates a valueprovided in an experiment using an actual plane (under conditions of aMach number in a range of 0.62 to 0.64 and a Reynolds number in a rangeof 11.5 to 16.7×10⁶); the square indicates a value provided in anexperiment using a transonic wind tunnel (under conditions of a Machnumber of 0.64 and a Reynolds number of 8×10⁶); and the triangleindicates a value in an experiment using the same transonic wind tunnel(under conditions of a Mach number of 0.7 and a Reynolds number of8×10⁶). The solid line and the broken line each indicate a theoreticvalue provided by a technique (which will be referred hereinafter to asMSES) which comprises a combination of an Euler method and an e^(n)method and which is one of analysis techniques for the airfoil in ahigh-speed range with a shock wave and a drag divergence taken intoconsideration. The solid line corresponds to a case where the separationof the turbulent-flow boundary layer in the vicinity of the rear profileportion Cr is taken into consideration. The broken line corresponds to acase where the separation of the turbulent-flow boundary layer in thevicinity of the rear profile portion Cr is not taken into consideration.

As apparent from FIG. 4, it is understood that the results of the flightexperiment and the wind tunnel experiment coincide sufficiently with thetheoretic value in the MSES in which the separation of theturbulent-flow boundary layer is taken into consideration, and that thehead-lowering pitching moment is remarkably decreased, as compared withthe theoretic value in the MSES in which the separation of theturbulent-flow boundary layer is not taken into consideration.

The largest thickness of the laminar-flow airfoil according to thepresent embodiment (the thickness of the wing between the upper wingsurface Su and the lower wing surface S1) is 15% of the wing chordlength C, and hence the capacity of a fuel tank within the wing can beincreased sufficiently to ensure a required mileage.

As shown in FIGS. 5 and 6, a main wing of an airplane employing thelaminar-flow airfoil according to the present embodiment includes aleading edge structure 11 and a wing central structure 12, which areassembled separately from each other. The leading edge structure 11includes a leading edge spar 13 having a channel-shaped section, aplurality of ribs 14 coupled to a front surface of the leading edge spar13, and a skin 15 covering the leading edge spar 13 and the ribs 14. Theskin 15 and piano hinges 16 are fastened together by rivets 17 to a rearupper portion of the leading edge spar 13 facing the wing centralstructure 12.

The skin 15 and piano hinges 18 are fastened together by rivets 19 to arear lower portion of the leading edge spar facing the wing centralstructure 12.

The wing central structure 12 includes a front spar 20 having achannel-shaped section, a plurality of ribs 21 coupled to a rear surfaceof the front spar 20, and an upper skin 22 and a lower skin 23 coveringthe front spar 20 and the ribs 21. The upper skin 22 and the lower skin23 are fastened by rivets 24 and 25 to the front spar 20. Piano hinges26 are fastened by rivets 27 to a front upper portion of the front spar20 facing the leading edge structure 11. Piano hinges 28 are fastened byrivets 29 to a front lower portion of the front spar 20 facing theleading edge structure 11.

A rear surface of the leading edge structure 11 is abutted against afront surface of the wing central structure 12, and pins 30 are insertedthrough the piano hinges 16 and 18 of the leading edge structure 11 andthe corresponding piano hinges 26 and 28 of the wing central structure12, whereby the wing central structure 12 and the leading edge structure11 are integrally coupled to each other. At this time, it is unavoidablethat a small gap a and a small step β are generated between a rear endof the skin 15 of the leading edge structure 11 and front ends of theupper skin 22 and the lower skin 23 of the wing central structure 12 dueto an error in the manufacture.

A graph in FIG. 7 shows the amounts ΔCd of change in drag coefficient,in the case where a step was provided in the upper surface of thelaminar-flow airfoil according to the present embodiment. Specifically,a flight test was carried out using a real airplane with steps havingdifferent heights provided at positions corresponding to 10% and 20% ofthe wing chord length C in the upper surface of the main wing of thereal airplane, wherein amounts ΔCd of change in the drag coefficientwere calculated by comparison with that in a case where no step wasprovided. For example, when the step is 0.19 mm, it can be seen that theamount ΔCd of change in drag coefficient in the case where the step wasprovided at the position corresponding to 10% of the wing chord length Cis about 30 counts in a range of a Reynolds number smaller than 13×10⁶,while the amount ΔCd of change in drag coefficient in the case where thestep was provided at the position corresponding to 20% of the wing chordlength C is about 3 counts which is one tenth of the 30 counts in therange of a Reynolds number smaller than 13×10⁶. That is, the influenceof the step is dramatically reduced. When the Reynolds number is13.5×10⁶, the effect is somewhat reduced, but the amount ΔCd of changein drag coefficient in the case where the step was provided at theposition corresponding to 20% of the wing chord length C is remarkablydecreased to 7 counts from 30 counts shown in the case where the stepwas provided at the position corresponding to 10% of the wing chordlength C.

As described above, in the case where the laminar-flow airfoil accordingto the present embodiment is employed, if the step is disposed at theposition corresponding to 20% of the wing chord length C, an increase indrag can be minimized. Therefore, it is possible to minimize an increasein drag due to the gap a and the step β by disposing coupled portionsbetween the leading edge structure 11 and the wing central structure 12,in which the generation of the gap a and the step β are unavoidable, atthe position corresponding to 20% of the wing chord length C.

Although the embodiment of the present invention has been described indetail, it will be understood that the present invention is not limitedto the above-described embodiment, and various modifications in designmay be made without departing from the spirit and scope of the inventiondefined in the claims.

For example, the rear profile portion Cr has the negative curvatureradius in the embodiment, but may be rectilinear.

In addition, the largest-thickness position Tu on the upper wing surfaceSu is established at the position corresponding to 38% of the wing chordlength C in the embodiment, but may be established between a positioncorresponding to 30% of the wing chord length C and a positioncorresponding to 50% of the wing chord length C.

Further, even in an already existing airfoil which is not included inthe present invention, a similar effect can be expected, if such anairfoil is improved into an airfoil included in the present invention byproviding a padding on a surface of a wing having the airfoil or bygrinding such a surface.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A main wing structure comprising at least aleading edge structure and a wing central structure coupled to eachother, wherein said main wing structure has a laminar-flow airfoilcomprising an upper wing surface, a lower wing surface, a leading edgeand a trailing edge, said upper wing surface including: a front profileportion which has a positive curvature radius, and which is provided toextend from the leading edge to a largest-thickness point located in arange of 30% to 50% of a wing chord length; a central profile portionwhich has a positive curvature radius, and which is provided to extendfrom the largest-thickness point to the vicinity of a positioncorresponding to approximately 90% of the wing chord length at which avalue obtained by dividing a thicknesswise difference between theposition and the largest-thickness point by a distance in a direction ofa wing chord from the largest-thickness point is equal to or smallerthan 0.12; and a rear profile portion which has a negative curvatureradius, and which is provided to extend from the vicinity of a positioncorresponding to approximately 95% of the wing chord length to thetrailing edge, and wherein coupled portions between said leading edgestructure and said wing central structure are arranged at positionscorresponding to approximately 20% of the wing chord length.
 2. The mainwing structure according to claim 1, wherein the largest-thickness pointis approximately 38% of the wing chord length.
 3. The main wingstructure according to claim 1, and further including a transition pointat which the laminar-flow boundary layer region changes to aturbulent-flow boundary layer region.
 4. The main wing structureaccording to claim 3, wherein the transition point is approximately 42%of the wing chord length.
 5. The main wing structure according to claim1, and further including a largest-thickness position disposed on thelower wing surface for forming a laminar-flow boundary layer region. 6.The main wing structure according to claim 5, wherein thelargest-thickness position disposed on the lower wing surface isapproximately 49% of the wing chord length.
 7. The main wing structureaccording to claim 5, and further including a transition point disposedon the lower wing surface at which the laminar-flow boundary layerregion changes to a turbulent-flow boundary layer regions.
 8. The mainwing structure according to claim 7, wherein the transition pointdisposed on the lower wing surface is approximately 63% of the wingchord length.
 9. A main wing structure comprising at least a leadingedge structure and a wing central structure coupled to each other,wherein said main wing structure has a laminar-flow airfoil comprisingan upper wing surface, a lower wing surface, a leading edge and atrailing edge, said upper wing surface including: a front profileportion which has a positive curvature radius, and which is provided toextend from the leading edge to a largest-thickness point located in arange of 30% to 50% of a wing chord length; a central profile portionwhich is rectilinear a positive curvature radius, and which is providedto extend from the largest-thickness point to the vicinity of a positioncorresponding to approximately 90% of the wing chord length at which avalue obtained by dividing a thicknesswise difference between theposition and the largest-thickness point by a distance in a direction ofa wing chord from the largest-thickness point is equal to or smallerthan 0.12; and a rear profile portion which has a negative curvatureradius, and which is provided to extend from the vicinity of a positioncorresponding to approximately 95% of the wing chord length to thetrailing edge, and wherein coupled portions between said leading edgestructure and said wing central structure are arranged at positionscorresponding to approximately 20% of the wing chord length.
 10. Themain wing structure according to claim 9, wherein the largest-thicknesspoint is approximately 38% of the wing chord length.
 11. The main wingstructure according to claim 9, and further including a transition pointat which the laminar-flow boundary layer region changes to aturbulent-flow boundary layer region.
 12. The main wing structureaccording to claim 11, wherein the transition point is approximately 42%of the wing chord length.
 13. The main wing structure according to claim9, and further including a largest-thickness position disposed on thelower wing surface for forming a laminar-flow boundary layer region. 14.The main wing structure according to claim 13, wherein thelargest-thickness position disposed on the lower wing surface isapproximately 49% of the wing chord length.
 15. The main wing structureaccording to claim 13, and further including a transition point disposedon the lower wing surface at which the laminar-flow boundary layerregion changes to a turbulent-flow boundary layer regions.
 16. The mainwing structure according to claim 15, wherein the transition pointdisposed on the lower wing surface is approximately 63% of the wingchord length.
 17. A main wing structure comprising at least a leadingedge structure and a wing central structure coupled to each other,wherein said main wing structure has a laminar-flow airfoil comprisingan upper wing surface, a lower wing surface, a leading edge and atrailing edge, said upper wing surface including: a front profileportion which has a positive curvature radius, and which is provided toextend from the leading edge to a largest-thickness point located in arange of 30% to 50% of a wing chord length; a central profile portionwhich has a positive curvature radius, and which is provided to extendfrom the largest-thickness point to the vicinity of a positioncorresponding to approximately 90% of the wing chord length at which avalue obtained by dividing a thicknesswise difference between theposition and the largest-thickness point by a distance in a direction ofa wing chord from the largest-thickness point is equal to or smallerthan a predetermined number; and a rear profile portion which has anegative curvature radius or is rectilinear, and which is provided toextend from the vicinity of a position corresponding to approximately95% of the wing chord length to the trailing edge, and wherein coupledportions between said leading edge structure and said wing centralstructure are arranged at positions corresponding to approximately 20%of the wing chord length.
 18. The main wing structure according to claim17, wherein the largest-thickness point is equal to or smaller than0.12.
 19. The main wing structure according to claim 17, wherein thecentral profile portion extends to the vicinity of a positioncorresponding to approximately 90% of the wing chord length.
 20. Themain wing structure according to claim 17, wherein the rear profileportion extends to a position corresponding to approximately 95% of thewing chord length.